Two stage hemofiltration that generates replacement fluid

ABSTRACT

The present invention relates to a system for two-stage blood dialysis of a patient. In one embodiment, the system comprises a first filtration device for receiving the blood from the patient and for producing a first filtrate and processed blood. The system further comprises a second filtration device for receiving the first filtrate and producing replacement fluid and waste product. At least one of the first and second filtration devices preferably comprises a Taylor vortex-enhanced blood filtration device.

RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/922,763filed on Aug. 20, 2004, now U.S. Pat, No. 7,374,677, issued May 20,2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Preferred aspects of the present invention relate to multistepfiltrations wherein successive filtrations remove filtrates of variousspecifications. Preferred embodiments of the present invention areparticularly useful to regenerate fluid lost during blood dialysis.

2. Description of the Related Art

Traditionally, dialysis is the maintenance therapy used to treat kidneydisease. There are two common approaches. One is peritoneal dialysis,wherein the process is done internally to the patient, in the patient'spericardium. Peritoneal dialysis uses the patient's abdominal lining asa blood filter. The abdominal cavity is filled with dialysate, therebycreating a concentration gradient between the bloodstream and thedialysate. Toxins diffuse from the patient's blood stream into thedialysate, which must be exchanged periodically with fresh dialysate.

The second approach is by filtration dialysis. Filtration dialysisencompasses two main filtration techniques: hemodialysis andhemofiltration. Both operate extracorporeally by removing the patient'sblood, treating the blood to remove toxins, and returning the processedblood to the patient. Yet, each process functions by a differentphysical separation technique.

Hemodialysis effects removal of toxins from blood by diffusion. Thepatient's blood flows past one side of a membrane while dialysate flowspast the other side. The membrane selectively allows for the flux ofsmall molecules. Due to the concentration gradient between the blood andthe dialysate, small molecule toxins diffuse into the dialysate. At thesame time, nutrients, such as electrolytes and other chemicals, presentin the dialysate diffuse into the blood. The processed blood is thenreturned to the patient.

Hemofiltration effects removal of toxins from blood by convection. Thepatient's blood is passed through a filter that is permeable to plasmawater and, generally, molecules smaller than 20,000 Daltons. Theresulting plasma water filtrate, called “blood-waste,” contains water,the toxic blood components, and “small desirable molecules,” includingsmall molecule nutrients and electrolytes. Since the processed bloodlacks vital components lost through filtration, and since its volume issubstantially reduced, a replacement fluid must be added to theprocessed blood before its reintroduction to the patient. Depending onthe hemofiltration needs, the replacement fluid can be added pre- orpost-hemofiltration.

In addition to these two blood purification techniques, methodscombining hemodialysis and hemofiltration, known as hemodiafiltration,have been used. Hemodiafiltration effects removal of toxins from bloodby both diffusion and convection. As in hemofiltration, blood volume andnutrients/electrolytes must be replaced with replacement fluid inhemodiafiltration procedures.

Generally, replacement fluid is engineered to mimic healthy plasma waterwith respect to pH, electrolyte and nutrient concentration. However, thereplacement fluid may also be adjusted to correct for abnormalities inthe individual patient. Biologically compatible buffers, such ascitrate, lactate, acetate and bicarbonate, often serve as the base forreplacement fluids. The buffers may then be supplemented withelectrolytes, such as chloride, sodium, calcium, magnesium, potassium,and phosphate, and nutrients, such as glucose and dextrose, as requiredby the patient.

Disadvantages of these blood processing methods include the difficultiesand costs associated with the production of a large amount ofreplacement fluid that is free of contaminants harmful to the patient.In addition, hemodialysis, hemofiltration and hemodiafiltration create asubstantial amount of medical waste that is costly to dispose of.Consequently, there exists a need to recycle the waste from thesesystems to generate bio-compatible, low cost replacement fluid ordialysate. Thereby, the need for the production of large volumes offoreign dialysate or replacement fluid may be eliminated. Filtration ofthe patient's blood-waste generated during blood dialysis meets theseneeds.

Another problem faced by those using well-known methods of blooddialysis is filter clogging, described as “concentration polarization.”As a result of the selective permeability properties of a filter,filtered material that cannot pass through the filter often becomesconcentrated on the surface of the filter. This phenomenon is clearlyillustrated by the case of a “dead-end” filter, such as a coffee filter.During the course of the filtration process, the filtered material(coffee grounds) building up on the filter creates flow resistance tothe filtrate, the fluid (coffee), which can pass through the filter.Consequently, filtrate flux is reduced, and filtration performancediminishes.

Various solutions to the problem of concentration polarization have beensuggested. These include: increasing the fluid velocity and/or pressure(see e.g., Merin et al., (1980) J Food Proc. Pres. 4(3):183-198);creating turbulence in the feed channels (Blatt et al., Membrane Scienceand Technology, Plenum Press, New York, 1970, pp. 47-97); pulsing thefeed flow over the filter (Kennedy et al., (1974) Chem. Eng. Sci.29:1927-1931); designing flow paths to create tangential flow and/orDean vortices (Chung et al., (1983) J. Memb. Sci. 81:151-162); and usingrotating filtration to create Taylor vortices (see e.g., Lee and Lueptow(2001) J. Memb. Sci. 192:129-143 and U.S. Pat. Nos. 5,194,145,4,675,106, 4,753,729, 4,816,151, 5,034,135, 4,740,331, 4,670,176, and5,738,792, all of which are incorporated herein in their entirety byreference thereto). In U.S. Pat. No. 5,034,135, Fischel disclosescreating Taylor vorticity to facilitate blood fractionation. Fischelalso describes variations in the width of the gap between a rotaryspinner and a cylindrical housing, but does not teach variation in thiswidth about a circumferential cross-section.

Taylor vortices are induced in the gap between coaxially arrangedcylindrical members when the inner member is rotated relative to theouter member. Taylor-Couette filtration devices generate strongvorticity as a result of centrifugal flow instability (“Taylorinstability”), which serves to mix the filtered material concentratedalong the filter back into the fluid to be processed. Typically, acylindrical filter is rotated within a stationary outer housing. It hasbeen observed that membrane fouling due to concentration polarization isvery slow compared to dead-end or tangential filtration. Indeed,filtration performance may be improved by approximately one hundredfold.

The use of Taylor vortices in rotating filtration devices has beenapplied to the separation of plasma from whole blood (See, e.g., U.S.Pat. No. 5,034,135). For this application, the separator had to beinexpensive and disposable for one-time patient use. Further, theseseparators only had to operate for relatively short periods of time(about 45 minutes). Moreover, the separator was sized to accept the flowrate of blood that could reliably be collected from a donor (about 200ml/minute). This technology provided a significant improvement to theblood processing industry. The advantages and improved filtrationperformance seen with rotating filtration systems (Taylor vortices) havenot been explored in other areas of commercial fluidseparation—including kidney dialysis

Consequently, an improved blood dialysis system may be configured tosignificantly reduce the artificial replacement fluids necessary. Inaddition, this improved blood dialysis system may produce Taylorvortices to alleviate the problem of concentration polarization soprevalent with known methods of filtration.

SUMMARY OF THE INVENTION

In one embodiment, the present invention relates to a system fortwo-stage blood dialysis of a patient. The system comprises a firstfiltration device for receiving the blood from the patient and producinga first filtrate and processed blood. The system further comprises asecond filtration device for receiving the first filtrate and producingreplacement fluid and waste product. At least one of the first andsecond filtration devices preferably comprises a Taylor vortex-enhancedblood filtration device.

In another embodiment, the present invention relates to another systemfor two-stage blood dialysis of a patient. The system comprises adialysis device for receiving the blood from the patient and dialysateand producing waste dialysate and processed blood. The system furthercomprises a filtration device for receiving the waste dialysate andproducing recycled dialysate and waste product.

In another embodiment, a method for performing hemodialysis on a patientmay be implemented in accordance with the present invention. A firstfiltration device configured to create Taylor vorticity is provided, anda second filtration device is also provided. Blood is introduced fromthe patient into the first filtration device, and a first filtrate fromthe first filtration device is introduced into the second filtrationdevice. A replacement fluid may then be obtained from the secondfiltration device.

In another embodiment, a second method for performing hemodialysis on apatient may be implemented in accordance with the present invention. Afirst filtration device is provided, and a second filtration deviceconfigured to create Taylor vorticity is also provided. Blood isintroduced from the patient into the first filtration device, and afirst filtrate from the first filtration device is introduced into thesecond filtration device. A replacement fluid may then be obtained fromthe second filtration device.

In another embodiment, another method for performing hemodialysis on apatient may be implemented in accordance with the present invention. Adialysis device and a filtration device are provided. Blood isintroduced from the patient into the dialysis device, and wastedialysate from the dialysis device is introduced into the filtrationdevice. A recycled dialysate may then be obtained from the filtrationdevice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross sectional view of one embodiment of avortex-enhanced blood dialysis device for use with the presentinvention.

FIG. 2 shows an overhead cross sectional view of one embodiment of thedevice of FIG. 1.

FIG. 3 shows an overhead cross sectional view of a second embodiment ofa vortex-enhanced dialysis device.

FIG. 4 shows an overhead cross sectional view of a third embodiment of avortex-enhanced dialysis device.

FIG. 5 shows a cross sectional view of one embodiment of a dual rotorvortex-enhanced device of the present invention.

FIG. 6 shows the cross-sectional view of FIG. 5, with the flow-paths ofthe blood (outer gap) and dialysate (inner gap) highlighted.

FIG. 7 a shows a schematic illustration of a filtration dialysis system,wherein replacement fluid is generated from the patient's blood-wasteand combined with the blood being drawn from the patient.

FIG. 7 b shows a second schematic illustration of a filtration dialysissystem, wherein the replacement fluid is generated from the patient'sblood-waste and combined with processed blood prior to returning to thepatient.

FIG. 8 shows a schematic illustration of a filtration dialysis system,wherein recycled dialysate is obtained from waste dialysate flowing froma dialysis device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Traditionally, blood dialysis procedures are single stage. In otherwords, the blood is removed from the patient, processed through a singlefiltration device to remove waste products, and returned to the patient.Unfortunately, blood is a heterogeneous fluid with molecules that areboth smaller and larger than these waste products, which are generallyin the range of 300-6,000 Daltons. As a result, filtration devices thatremove the waste products from blood often inadvertently remove many ofthose smaller molecules, e.g. water and electrolytes, in the process.These smaller molecules must then be replaced prior to reintroduction ofthe blood to the patient.

In typical machines, blood is pumped from the patient at 300-450 mL/min.Approximately half of this flow is filtered from the blood and disposedof as blood-waste. In a 3 hour procedure, between 20 and 30 liters ofreplacement fluid must therefore be added to the blood flow in order tokeep the patient's blood volume constant. Of course, the majority of thefiltrate in such a procedure comprises water and other small, desirablemolecules.

One embodiment of the present invention contemplates using a multi-stagefiltration process to recapture much of this desirable filtrate andcombine it with the processed blood in order to improve the blood volumereturning to the patient without using excessive volumes of artificialreplacement fluid. In one embodiment, a two-stage filtration process isemployed. In the first stage, a filtration device, like that in theprior art, is used that is permeable to water, small nutrient moleculesand waste products. In the second stage, blood-waste emerging from thisfirst stage filtration device is sent through a second filtration devicethat filters the larger waste product molecules. The plasma waterfiltrate emerging from the second filtration device can then be used asclean, bio-compatible replacement fluid to increase the blood volumereturning to the patient. Of course, in other embodiments, more stagesmay be necessary to filter out particular waste products from other,similarly sized molecules.

A variety of filtration devices may be used to perform either the firstor second stages of one embodiment of the present invention. FIG. 1shows a cross section of one possible filtration device 10 to be used inthe present invention. In this filtration device, a single rotor createsTaylor vorticity. In the illustrated embodiment, the filtration device10 is used to perform hemodialysis, filtering molecules of a certainsize (including waste products) from blood. In other embodiments, thedevice 10 may be used, more generally, to transfer mass from one fluid.In still other embodiments, the device 10 may be used to transfer heatfrom one fluid. As would be well known to those of skill in the art, theinvention should not be limited to medical applications.

In one embodiment, the filtration device 10 comprises a cylindrical case12 housing a cylindrical rotor 14. A gap 16 exists between the case 12and the rotor 14, and, in a preferred embodiment, the rotor 14 isdisposed coaxially within the cylindrical case 12. In other embodiments,different geometries and configurations may be chosen for the case androtor, to accommodate other fluids and other means of generating Taylorvorticity.

In the illustrated embodiment, the cylindrical, circumferential walls ofthe rotor 14 are at least partially composed of a filtration membrane18, and partially define a rotor interior 20. The rotor interior 20 isfurther defined by the top and bottom walls of the rotor 14, which mayor may not comprise filtration membrane. As illustrated in FIG. 1, thefiltration membrane 18 may be used for the first stage of a two-stagedialysis method. The filtration membrane acts as a dialysis membrane,porous to water, electrolytes, small nutrient molecules and the small tomedium-sized molecules that make up waste products present in blood. Ina typical application, the dialysis membrane 18 is porous up to a massof approximately 10,000 Daltons. In another application, the dialysismembrane 18 may be more or less porous, in the range of 6,000 to 20,000Daltons. In another embodiment, the filtration membrane may be used forthe second stage of the two-stage dialysis method. The filtrationmembrane might then be permeable for molecules up to a mass ofapproximately 300 Daltons. Thus, plasma water, electrolytes and smallnutrient molecules would flow through as filtrate into the rotorinterior 20, and the heavier waste products would be filtered out. Inother embodiments, varying degrees of filtration and/or heat transfermay be facilitated by the use of different filtration membranes. Forexample, in a heat transfer application, the filtration membrane maycomprise an impermeable structure, which nevertheless is an effectivetransferor of heat.

In the illustrated embodiment, the cylindrical case 12 has three fluidaccess ports 22, 24, 26; two 22, 24 leading to and from the gap 16between the case 12 and rotor 14, and one 26 leading from the rotorinterior 20. In other embodiments, different fluid access configurationsmay be provided. For example, in one embodiment, only one fluid accessport leads to the gap between the case and rotor, and two ports may leadto the rotor interior.

In one embodiment, mounted in the axis A of the cylindrical case 12 aretwo pivot pins 30, 32, one on either end. These pivot pins 30, 32 definethe axis of rotation A for the rotor 14 and facilitate the free rotationof this rotor 14. As illustrated, the bottom pivot pin 32 may be hollow,allowing fluid transport passage through the case 12 and rotor 14. Ofcourse, in other embodiments, the top pivot pin 30 may also be hollow toaccommodate another fluid access port. Other means of facilitatingrotation may be provided, including, e.g., ball-bearing assemblies andother means well known to those of skill in the art.

In one embodiment of the invention, the rotor 14 can rotate freelywithin the cylindrical case 12. In order to control this rotation, aspinner magnet 34 may be mounted internally to the rotor 14, and anexternal rotating magnetic field (not shown) may be configured tointeract with this spinner magnet 34. By modulating the externalmagnetic field, the magnet 34 and, in turn, the rotor 14 can be made tospin in different directions and at varying speeds. In a preferredembodiment of the invention, the rotor 14 can be spun at a speedsufficient to create Taylor vorticity within a fluid in the gap 16between the rotor 14 and case 12. By creating Taylor vorticity in thisgap 16, filtration performance can be dramatically improved. Other meansof spinning the rotor 14 in order to create Taylor vorticity may be usedin keeping with this invention, as is known to those of skill in theart. For example, in one embodiment, a motor may be attached to at leastone of the pivot pins, e.g. the top pivot pin 30, attached to the rotor14.

In one embodiment, the rotating magnetic fields that control the rotor14 can be produced by a series of magnetic coils that surround thefiltration device 10 at its top. These electrical coil assemblies can beformed in half arch (“C” sections) that can be closed around the device10, although other configurations are possible.

The illustrated size of the device 10 is considered adequate forhemodialysis, although in other applications, larger or smallerfiltration devices may be utilized to suit the particular fluids beingprocessed.

In a hemodialysis application, the gap 16 between the rotor 14 andinside wall of the case 12 is selected to provide adequate Taylorvorticity in the blood. This gap 16 depends on the diameter and the RPMof the rotor 14, which parameters can be modified by one of skill in theart. With a centrifugal speed in the range of about 2000-5000 RPM and arotor diameter of about 0.1 to 10 inches, the width adequate to generateTaylor vortices may be in the range of about 0.003 to about 0.3 inches.More preferably, a gap 16 having a width of about 0.03 inches shouldprovide adequate vorticity for a rotor 14 of about 1 inch in diameterspun at about 2,400 RPM. In a preferred embodiment of the filtrationdevice 10, the rotor has a diameter of approximately 2 inches and isslightly longer than 6 inches.

FIGS. 2-4 illustrate some further structural features of differentembodiments of the hemodialysis device described above for use in thetwo-stage filtration process. In particular, different geometries andconfigurations of the housing and rotor are shown, which may beimplemented to attain various advantages. In FIG. 2, the embodimentdescribed above is shown. As can be more clearly seen in this Figure,the rotor 14 is cylindrical and disposed coaxially within thecylindrical case 12. Thus, the gap 16 is of constant width about thecircumference of the device 10. In this relatively simple embodiment,calibrating the appropriate speed of the rotor 14 is more easilyaccomplished, and the Taylor vortices are fairly constant in strengthabout the entire filtration membrane 18.

In FIG. 3, another configuration of the case 12 and rotor 14 is shown.In this embodiment, the case 12 and rotor 14 have individualcross-sections similar to those in FIG. 2, but are no longer alignedcoaxially. As shown in FIG. 3, the gap 16 therefore varies in widthabout the circumference of the case 12. Since the Taylor number,reflecting the strength of resulting vortices, is directly proportionalto the width of the gap, the sections of rotor 14 farther from the wallof the case 12 experience greater Taylor vorticity than those sectionsnearer to the wall. As the rotor 14 passes these wider gap locations,residual concentration polarization and any clogging of the filtermembrane 18 will be “blown” off by the stronger vortices, opening upblinded zones in the membrane 18. As a result, once per revolution, thelongitudinally extending sections of the membrane 18 will be “cleaned”by passing the widened portions of the gap 16, and the efficiency of thedevice 10 may be improved. In addition, where the width of the gap 16decreases, the shear forces in the gap increase, and this varying shearforce may also tend to increase mass transport across the membrane 18.Thus, once per revolution, we can increase shear and decrease vorticityat any point on the membrane 18 on rotor 14.

In FIG. 4, another configuration of the case 12 and rotor 14 is shownthat will similarly create a non-constant width gap. In thisconfiguration, the case 12 and rotor 14 are configured similarly tothose in FIG. 2, but the case 12 further has a bulge 42 incorporatedinto its wall. The gap 16 therefore varies in width about thecircumference of the case 12, widening at the site of the bulge 42,producing the advantages discussed above with reference to FIG. 3. Theabrupt shift between wide and narrow widths in this embodiment mayintroduce further vortex characteristics that may facilitate dialysis.In other embodiments, the case 12 and rotor 14 may have othercross-sectional geometries, resulting in a variable width gap 16.

Returning to FIG. 1, one method of implementing the hemodialysis device10 may be discussed with reference to the Figure. Arrows 36, 38 and 40show the input and output of the flows into and out of the device 10. Inthe illustrated embodiment, blood from a patient flows through the gap16 between the rotor 14 and the case 12, while water, small nutrientmolecules, electrolytes and waste products are filtered into the rotorinterior 20. Due to the concentration gradient between the blood and theplasma water that initially crosses the membrane 18, certain wasteproducts will preferentially flow through the dialysis membrane 18 intothe plasma water, thereby dialyzing the blood. The rotor 14 spins at aspeed sufficient to create Taylor vortices in the blood and preventsconcentration polarization in the blood near the dialysis membrane 18.In this way, one embodiment of the present invention enables use of asmaller, more biocompatible hemodialysis device 10.

In further detail, a blood inlet port 22 is located at the top of thecylindrical case 12 and a blood outlet port 24 is located at the bottom.This allows blood to flow from top to bottom simply using gravitationalenergy, and pressure from the blood influx. The device 10 is preferablydesigned such that in the time it takes a certain quantity of blood totravel from the top of the hemodialysis device 10 to the bottom, thedesired amount of waste by-product has been extracted. A water and wasteby-product outlet port 26 is located at the bottom of the rotor 14. In apreferred embodiment, this solution flows out of the device 10 forfurther filtering as described in further detail below.

In another embodiment, a dialysis fluid may be used to facilitatehemodialysis. Another fluid access port may be added to the top of thedevice 10 to allow dialysis fluid to enter the device. As is describedin detail with reference to FIG. 6, waste products diffuse into thedialysis fluid and are carried away from the device by the dialysateflow. Other modifications may also be made in keeping with the presentinvention.

FIG. 5 shows a cross section of another possible embodiment for use withthe present invention, in which a dual rotor device creates Taylorvorticity. This illustrated device may preferably be used in a two-stageblood dialysis system, such as that described in detail with referenceto FIG. 8. In the illustrated embodiment, the filtration device 110 isused to perform hemodialysis, filtering undesirable waste products fromblood into a dialysis fluid, or “dialysate.” In other embodiments, thedevice 110 may be used, more generally, to transfer mass from one fluidto another. In still other embodiments, the device 110 may be used totransfer heat from one fluid to another. As would be well known to thoseof skill in the art, the invention should not be limited to medicalapplications.

In one embodiment, the filtration device 110 comprises a cylindricalcase 112 housing a cylindrical outer rotor 114. A first gap 116 existsbetween the case 112 and the outer rotor 114 through which blood flows,and, in a preferred embodiment, the outer rotor 114 is disposedcoaxially within the cylindrical case 112. In other embodiments,different geometries and configurations may be chosen for the case androtor, as discussed above with reference to FIGS. 2-4.

In the illustrated embodiment, the cylindrical, circumferential walls ofthe outer rotor 114 are at least partially composed of a filtrationmembrane 118, and partially define an outer rotor interior 120. Theouter rotor interior 120 is further defined by the top and bottom wallsof the outer rotor 114, which may or may not comprise filtrationmembrane. As illustrated in FIG. 5, the filtration membrane 118 is adialysis membrane. This dialysis membrane 118 preferably facilitates thediffusion of molecules smaller than approximately 10,000 Daltons, andthe device 110 may thereby function as the first-stage device in thetwo-stage blood dialysis system illustrated in FIG. 8. In otherembodiments, varying degrees of filtration and/or heat transfer may befacilitated by the use of different filtration membranes. For example,in a heat transfer application, the filtration membrane may comprise animpermeable structure, which nevertheless is an effective transferor ofheat.

In one embodiment, mounted in the axis A of the cylindrical case 112 aretwo pivot pins 130, 132, one on either end. These pivot pins 130, 132define the axis of rotation A for the outer rotor 114, and facilitatethe free rotation of this rotor 114. As illustrated, the pivot pins 130,132 may also be hollow, providing fluid transport passages through thecase 112 and outer rotor 114. In other embodiments, other means offacilitating rotation may be provided, including, e.g., ball-bearingassemblies and other means well known to those of skill in the art.

In one embodiment of the invention, the outer rotor 114 can rotatefreely within the cylindrical case 112. In order to control thisrotation, a spinner magnet 134 may be mounted internally to the outerrotor 114, and an external rotating magnetic field (not shown) may beconfigured to interact with this spinner magnet 134. By modulating theexternal magnetic field, the magnet 134 and, in turn, the outer rotor114 can be made to spin in different directions and at varying speeds.In a preferred embodiment of the invention, the outer rotor 114 can bespun at a speed sufficient to create Taylor vorticity within a fluid inthe first gap 116 between the outer rotor 114 and case 112. By creatingTaylor vorticity in this first gap 116, filtration performance can bedramatically improved. Other means of spinning the outer rotor 114 inorder to create Taylor vorticity may be used in keeping with thisinvention, as is known to those of skill in the art. For example, in oneembodiment, a motor may be attached to at least one of the pivot pins,e.g. upper pivot pin 130, attached to the outer rotor 114.

Inside the outer rotor 114, an inner rotor 144, also supported by theupper and lower pivot pins 130, 132, may be mounted coaxially, with asecond gap 146 created between the two rotors 114, 144. Although theinner rotor 144 may partially comprise another filtration membrane, in apreferred embodiment, the inner rotor is relatively impermeable, simplydefining the second gap between the two rotors 114, 144. As described infurther detail above with respect to the outer rotor and case, the innerrotor 144 may also have differing cross-sectional geometries, and may bemis-aligned to accommodate other fluids and other means of generatingTaylor vorticity. In these alternative embodiments, the inner rotor 144may be supported by structures other than those supporting the outerrotor 114, and may spin about a different axis.

In a preferred embodiment, the inner rotor 144 rotates freely withinboth the outer rotor 114 and cylindrical case 112. In order to controlthis rotation, a second spinner magnet 148 may be mounted internally tothe inner rotor 144, and a second external rotating magnetic field (notshown) may be configured to interact with this second spinner magnet148. In the illustrated embodiment, the second spinner magnet 148 forthe inner rotor 144 is located at the top of the device 110, and thespinner magnet 134 for the outer rotor 114 is located at the bottom ofthe device 110. Thus, two separate and independent magnetic fields cancontrol the rotation of the two rotors 114, 144. As described in furtherdetail above, the second spinner magnet 148 mounted to the inner rotor144 may be controlled similarly to the one mounted to the outer rotor114. In a preferred embodiment, the inner rotor 144 can be spun at aspeed sufficient to create Taylor vorticity within a fluid in the secondgap 146 between the inner and outer rotors. In a further preferredembodiment, the inner rotor 144 is spun in a direction opposite theouter rotor 114 to create even more powerful Taylor vortices. Bycreating Taylor vorticity in this second gap 146, filtration performancecan be further improved, as concentration polarization is prevented onthe side of the filtration membrane 118 facing the inner rotor 144.Other means of spinning the inner rotor 144 in order to create Taylorvorticity may be used, as is known to those of skill in the art. Forexample, in one embodiment, a motor may be attached to at least one ofthe pivot pins, e.g. lower pivot pin 132, attached to the inner rotor144.

In one embodiment, the rotating magnetic fields that control the tworotors can be produced by a series of magnetic coils that surround thefiltration device 110 at its top and bottom. Since pre-connected tubing(not shown) enters and exits the device 110 on axis A in the illustratedembodiment, these electrical coil assemblies can be formed in half arch(“C” sections) that can be closed around the device 110.

The illustrated size of the device 110 is considered adequate forhemodialysis, although in other applications, larger or smallerfiltration devices may be utilized to suit the particular fluids beingprocessed.

In a hemodialysis application, the first gap 116 between the outer rotor114 and inside wall of the case 112 is selected to provide adequateTaylor vorticity in the blood. This first gap 116 depends on thediameter and the RPM of the outer rotor 114, which parameters can bemodified by one of skill in the art. With a centrifugal speed in therange of about 1000-5000 RPM and an outer rotor diameter of about 0.1 to10 inches, the width adequate to generate Taylor vortices may be in therange of about 0.003 to about 0.3 inches. More preferably, a first gap116 having a width of about 0.03 inches should provide adequatevorticity for an outer rotor 114 of about 1 inch in diameter spun atabout 2,400 RPM.

In the illustrated embodiment, the second gap 146 between the inner andouter rotors is selected to provide adequate Taylor vorticity in thedialysate. This second gap 146 depends on the diameters and the RPMdifference between the inner and outer rotors. With a centrifugal speedin the range of about 1000-5000 RPM and an inner rotor diameter of about0.1 to 10 inches, the width adequate to generate Taylor vortices betweenthe inner rotor 144 and outer rotor 114 may be in the range of about0.003 to about 0.3 inches. Preferably, a second gap 146 having a widthof about 0.03 inches should create adequate vorticity for an inner rotordiameter of about 0.8 inches spun at about 3,600 RPM. This preferred setof parameters would give a rotating speed of the inner rotor 144relative to the outer rotor 114 of about 1,200 RPM. Alternatively, byspinning the inner rotor 144 in the opposite direction of the outerrotor 114, powerful Taylor vorticity can be created in the dialysate.

For the various potential applications, the dimensions and speeds of theinner and outer rotors and casing may be dramatically different. Forexample, in certain industrial applications, the filtration device 110may be designed on a much larger-scale in order to accommodate largerflows and liquids of varying viscosity. Optimizing the ranges of gap androtor sizes, as well as centrifugal speed and rotor direction can bedone by one of skill in the art based on the teaching herein.

In the illustrated embodiment, the cylindrical case has four fluidaccess ports 122, 124, 126, 128. A first inlet port 122 is located atthe top of the cylindrical case 112, and a first outlet port 124 islocated at the bottom. In a hemodialysis application, this allows bloodto flow from top to bottom through the first gap 116 simply usinggravitational energy, and pressure from the blood influx. The device 110is preferably designed such that in the time it takes a certain quantityof blood to travel from the top of the hemodialysis device 110 to thebottom, the desired amount of waste by-product has been extracted. Asecond inlet port 126 is located at the bottom of the outer rotor 114,and a second outlet port 128 is located at the top of the outer rotor114. In the hemodialysis application, the dialysis fluid flows throughthese ports from the bottom of the device 110 to the top through thesecond gap 146 between the inner and outer rotors. In this preferredembodiment, the fluid paths are designed to take advantage ofcounter-current mass transfer, meaning that the paths of blood anddialysate are opposite. Fresh dialysate is exposed through the dialysismembrane 118 with mostly dialyzed blood, where the concentrationgradient is the lowest. As is well known to those of skill in the art,however, other numbers and configurations of fluid access ports may beused in keeping with the present invention.

Since the first inlet and outlet ports 122, 124 are on the outerdiameter of the case 112, there is no need for high pressure on thatflow path. This being the case, in the illustrated embodiment, bloodwill not be forced to the center of rotation of the outer rotor 114,thus fluid seals are not necessary there to prevent blood from enteringthe inner rotor 144. Fluid seals can be added if higher fluid pressuresare employed in hemodialysis or other applications, or if fluids forfiltering enter the inner rotor 144 for any reason.

In a preferred embodiment, the second inlet port 126 for dialysate isconfigured so that the dialysate passes through the lower pivot pin 132and is then directed into the second gap 146 between the inner and outerrotors, and not downward into the first gap 116 between the outer rotor114 and case 112. A fluid seal 150 at the top pivot pin 130 is includedin the illustrated embodiment to prevent migration of dialysate into thefirst gap 116 between the outer rotor 114 and case 112. This seal 150can be any conventional polymer lip seal. As is well known to those ofskill in the art, other seals may be implemented. In an alternativeembodiment, another fluid seal is included at the bottom pivot pin 132.

In one method of practicing the present invention, blood is exposed tothe dialysis membrane 118 with Taylor vorticity resulting in a minimalconcentration polarization layer in the first gap 116 between the outerrotor 114 and case 112, maximizing the ability to remove low molecularweight waste products from the patient's blood. In the process ofpassing through the filtration device 110, dialysate is also exposed toTaylor vorticity, resulting in a minimal concentration polarizationlayer near the interior of the dialysis membrane 118, maximizing theability to mix the low molecular weight waste products into thedialysate flow. In a preferred embodiment, the waste dialysate emergingfrom the device 110 may then be directed through another filtrationdevice to produce recycled, clean dialysate.

In connection with FIG. 6, an exemplary method of performinghemodialysis will be described using the device described in FIG. 5.Within the device 110, the inner and outer rotors are spinning inopposite directions at speeds sufficient to create Taylor vortices influids between the outer rotor 114 and case 112, and between the innerrotor 144 and outer rotor 114. Blood is collected from the patient at aparticular flow rate 136, and enters the hemodialysis device 110 throughthe blood inlet port 122, located at the top of the device 110. Dialysisfluid also enters the hemodialysis device 140, but from the bottom,through a second, dialysate inlet port 126. The two fluids are subjectedto the forces from the rotors, and Taylor vortices form within them.Thus, concentration polarization is largely alleviated at the dialysismembrane 118 of the outer rotor 114, and a more constant flow of wasteproducts travels through the membrane 118 into the dialysate. Thedialysate travels through the hemodialysis device 110, within the secondgap 146 between the outer and inner rotors, and exits the top through adialysate outlet port 128, while the processed blood exits through theblood outlet port 124 at the bottom of the device 110 and is returned tothe patient.

In other embodiments, other Taylor vortex-enhanced filtration devicesmay be used, as further discussed in the co-pending U.S. patentapplication Ser. No. 10/797,510, which application is hereinincorporated by reference in its entirety.

One problem with many of the above described methods of hemodialysis isthat the dialysis membrane may be porous to water as well as wasteproducts. Thus, large volumes of plasma water accompany waste productstraveling through the dialysis membrane, and the flow of processed bloodexiting through the blood outlet port is dramatically reduced from theblood entering the hemodialysis device. This problem is especially acutewith respect to the filtration device 10 illustrated in FIG. 1. In oneembodiment, a sterile replacement fluid may be added to the processed,dialyzed blood at a junction prior to return to the patient. However,this embodiment risks patient exposure to contaminated replacementfluid, and increases the costs of hemodialysis by the cost of thereplacement fluid.

FIGS. 7A and 7B are schematic illustrations of alternate embodiments oftwo-stage blood dialysis systems according to the present invention,wherein replacement fluid is generated from the blood-waste emergingfrom a first stage filtration device, reducing the need for artificialreplacement fluid. The illustrated embodiments differ in the ordering ofsteps by which this goal is accomplished but share many operativefeatures. Therefore, the components of these two systems will bediscussed together, and the differences will be highlighted, asnecessary, in the following discussion. The directions of the flows ofvarious fluids flowing through the systems are illustrated by arrows.

A patient is represented by the box 200 farthest to the left. In atypical implementation, the patient 200 may have a kidney disease thatis producing uremic metabolic abnormalities. It is believed that this isdue to the fact that intermediate molecular weight molecules (300-6,000Daltons), removed by healthy kidneys, are producing a morbid toxicity inthese patients. In order to alleviate this accumulated toxicity, such apatient 200 typically undergoes periodic dialysis procedures, whichremove these intermediate weight molecules. In other embodiments, it maybe understood by those of skill in the art that the patient 200 may haveanother disease in which dangerous or harmful substances are present inthe patient's blood. In still other embodiments, the source of the fluidthat will be filtered need not be a patient. The process may be used inan industrial setting, for example, in which the fluid is someheterogeneous mixture from which intermediate sized molecules must beextracted.

The device used for the first stage of this two-stage blood dialysissystem may be described as a blood filtration device 210. As describedabove, such a device 210 generally produces filtrates of moleculessmaller than a certain size. As is well-known to those of skill in theart, the filtration membrane used in the device 210 can have a widevariety of characteristics and can be chosen to filter any of a numberof different sized particles. In one embodiment, the blood filtrationdevice 210 is configured to filter out those molecules having a weightof 10,000 Daltons or less. In this embodiment, the filtrate willpreferably include those intermediate weight molecules that are toxic tothe patient 200.

The device used for the second stage of this two-stage blood dialysissystem may be described as an ultrafiltration device 220, so calledbecause it is permeable to smaller molecules. In a preferred embodiment,the purpose of the ultrafiltration device 220 is to filter out theintermediate weight, toxic molecules from a heterogeneous solution,leaving only water and other small desirable molecules. In the preferredembodiment, the filtration membrane used in the ultrafiltration device220 is chosen to allow molecules having a weight less than approximately300 Daltons to pass, thereby separating the potentially toxic wasteproducts from the rest of the solution. In other embodiments, thefiltration membrane may only allow molecules having a weight less thanapproximately 200 Daltons to pass, preventing other, questionably toxicmolecules from emerging as filtrate.

The same or different types of filtration devices may be used for theblood filtration device 210 and ultrafiltration device 220. They maycomprise, for example, conventional hollow fiber dialysis membranecartridges, or other filtration devices well known to those of skill inthe art. In a preferred embodiment, the devices are Taylorvortex-enhanced filtration devices that function similarly to thefiltration device 10 described above with reference to FIG. 1. Asdescribed above, these filtration devices may have any combination of avariety of sizes, shapes and speeds for their respective rotors andhousings, in order to accommodate the different viscosities and flowrates of the processed fluids.

A waste bag 230 is used to collect the undesirable waste productsproduced by this two-stage blood dialysis system. In one embodiment,this waste bag 230 should collect many of the same waste products thatwould normally be collected by a healthy kidney. Of course, the wastebag 230 may represent any of a number of means for collecting and/ordisposing of waste and need not be a physical receptacle of anyparticular shape or size. Often, the waste bags 230 must be collected ashazardous waste for careful disposal according to applicable laws andregulations. Due to the unique features of the present invention, thevolume of the waste products generated by the two-stage blood dialysissystem may be far less than that generated by a typical single-stagedialysis procedure.

Supplemental replacement fluid sources 240 are also shown in FIGS. 7Aand 7B, although they are shown at different locations in the twosystems. Although much of the replacement fluid necessary to keep thepatient's blood volume constant may be generated from the patient's ownblood-waste, there may remain a need for relatively small amounts ofartificial replacement fluid during the procedure. Even if the two-stagefiltration system functioned perfectly, the volume represented by theintermediate-weight waste molecules should typically be replaced inorder to keep the patient's blood volume constant. In one embodiment, itis estimated that approximately three liters of artificial replacementfluid must be added to the patient's blood flow every three hours, asapproximately three liters of waste products are removed over the sametime frame. This would represent a significant improvement over the20-30 liters needed during a typical procedure, as described above.

The supplemental, artificial replacement fluid may be generated in anumber of ways, but must be sterile, pyrogen-free and generally at bodytemperature. In one embodiment, artificial replacement fluid may beproduced from common tap water as shown in “Successful Production ofSterile Pyrogen-Free Electrolyte Solution by Ultrafiltration,” KidneyInternational, 14, 522-25, 1978, a paper by Lee Henderson and ErminiaBeans, which is hereby incorporated by reference in its entirety. Inother embodiments, such fluid may be produced by other methods wellknown to those of skill in the art.

In FIG. 7A, an optional component of a two-stage blood dialysis systemis shown: an anticoagulant source 250. This anticoagulant source 250 maycomprise a source for heparin, for example, that is mixed with blood toprevent the blood from coagulating extracorporeally. In otherembodiments, other means for facilitating filtration, and for preventingclumping or other undesirable fluid characteristics may be employed. Forexample, water may be added to other heterogeneous solutions tofacilitate the production of vortices in the filtration devices 210,220.

Using the two-stage blood dialysis system illustrated in FIG. 7A, amethod of performing blood dialysis according to the present inventionmay now be discussed in further detail. The first step in the procedureis drawing blood from the patient, illustrated by the arrow 255extending from the patient 200 to the blood dialysis filtration device210. Conventionally, blood is drawn from the patient 200 via an IV tubeconnected to a patient's artery in the patient's arm. Of course, othermeans of drawing blood from a patient are well-known to those of skillin the art. As discussed above, a typical rate of blood flow from thepatient is 300-450 mL/min. In order to keep the patient's blood volumerelatively constant, therefore, the fluid returning to the patient,arrow 265, must flow at a similar rate. Conventionally, the fluidreturning to the patient 200 is returned through an IV tube connected tothe patient's vein.

In an optional second step, the blood flowing from the patient 200 ismixed with an anticoagulant from an anticoagulant source 250. In thisway, performance of the blood dialysis system may be improved.

The blood that is flowing from the patient 200 is then passed throughthe blood dialysis filtration device 210. The filtration device 210 mayfilter the blood in a number of ways well known to those of skill in theart. In a preferred embodiment, the filtration device 210 workssimilarly to the device 10 described in detail above. In thisimplementation, the blood flows into the gap 16 between the case 12 andthe rotor 14 through the inlet port 22. The filtration membrane 18 isdesigned to allow molecules with a molecular weight less thanapproximately 10,000 Daltons to pass into the rotor interior 20. Theblood flowing from the patient 200 has a number of constituents,including: water, electrolytes, small nutrient molecules, wasteproducts, high molecular weight molecules (e.g. proteins, etc.) andblood cells and other cells of various types. The first four of theabove-listed constituents comprise blood-waste and can pass through thefiltration membrane 18 into the rotor interior 20. Thus the rotorinterior fills with water, electrolytes and small nutrient molecules,and waste products.

Meanwhile, the rotor 14 spins rapidly enough to create Taylor vorticesin the blood flowing through the gap 16 between the rotor 14 and housing12. These Taylor vortices mix the blood in this gap 16 and therebyalleviate the problem of concentration polarization on the outsideportion of the filtration membrane 18.

The filtration device 210 has two outlet ports, 24 and 26. The firstoutlet port 24 communicates with the gap 16 between the rotor 14 andhousing 12. If the blood-waste were not recycled, the blood constituentsthat were too large to pass through the filtration membrane 18 wouldpass out of the blood filtration device 210 through the outlet port 24.In a typical implementation, the flow rate from this outlet port 24would be roughly half the flow rate going into the inlet port 22. Thus,roughly half of the patient's blood comprises water, small desirablemolecules, and waste products, and the other half comprises largermolecules and cells which pass out through outlet port 24. These largercomponents would be represented by the arrow 265 leading back to thepatient 200.

However, since the water and small desirable molecules are recycled backinto the two stage system as replacement fluid, as shown by the arrow275, the blood filtration device 210 is unable to filter the incomingfluid completely, and the arrow 265 representing the processed blood andreplacement fluid returning to the patient comprises a volume at leastroughly equivalent to the blood flow 255 coming from the patient 200.The return flow 265 thereby comprises both larger components andreplacement fluid without undesirable waste products. Further details ofthis process are discussed below.

The second outlet port 26, which is in communication with the rotorinterior 20, conducts a flow 285, roughly half that of the blood flow255 from the patient, comprising water, small desirable molecules, andwaste products. This flow of blood-waste 285 enters the ultrafiltrationdevice 220.

As described above, the ultrafiltration device 220 may functionsimilarly to the filtration device 10. The filtration membrane 18 of theultrafiltration device 220 is configured such that water and smalldesirable molecules enter the rotor interior 20 of the ultrafiltrationdevice 220. The intermediate weight waste products are filtered out andpass from the ultrafiltration device 220 to the waste bags 230, asrepresented by the arrow 285. The filtrate, meanwhile, now comprises aclean, warm, bio-compatible replacement fluid that can be used toincrease the volume of blood that is returning to the patient.

In the embodiment shown in FIG. 7A, this patient-generated replacementfluid flow 275 is recycled to the beginning of the two-stage filtrationsystem, where a T-junction mixes the replacement fluid flow 275 and theflow from the patient 255. The T-junction may be any of a number ofdevices that mix two fluid inputs and have one fluid output, as is wellknown to those of skill in the art. In one embodiment, the T-junctionsimply comprises T-shaped sections of tubing. The amount of fluidentering the blood dialysis device 210 is thereby increased, and theflow 265 back to the patient 200 is also increased. Since there may be areduction in flow due to the loss of waste products, a small amount ofartificial, supplemental replacement fluid 240 may also be introduced.According to a preferred embodiment of the present invention, the flow265 returning to the patient 200 approximates the flow 255 exiting thepatient 200, and the patient's blood volume is kept relatively constant.

In a preferred embodiment, the replacement fluid can be supplementedwith a variety of additives. Typical additives include biologicallycompatible buffers, such as bicarbonate, lactate, citrate, and acetate.Other components, such as chloride, sodium, calcium, magnesium,potassium, phosphate, dextrose, and glucose, or any other moleculerequired by the particular patient, may also be added to the replacementfluid.

The implementation illustrated in FIG. 7B, is very similar to the onedescribed above with respect to FIG. 7A. The sole difference lies in thelocation of the T-junction, at which the patient-generated replacementfluid flow 275 reenters the system. In FIG. 7B, this flow 275 iscombined with the flow of processed blood returning to the patient 200.Thus, the return flow 265 is increased to approximate the extractionflow 255, immediately before reintroduction to the patient. In apreferred embodiment, flow meters may be placed at various points in thetwo-stage systems of FIGS. 7A and 7B in order to monitor fluid flows,and to provide feedback regarding the need for supplemental artificialfluid, for example. As is well-known to those of skill in the art, avariety of flow meters may be used, provided that they are sterile andconfigured for use in a hospital environment.

In both of these Figures, the blood dialysis device 210 can utilizehemofiltration or hemodiafiltration, including continuous veno-venoushemofiltration and continuous arterio-venous hemofiltration.

Although FIGS. 7A and 7B describe continuous processes, it is to beunderstood that batch processes are embraced. Batch processes includeprocessing portions of blood removed from patients. The blood can thenbe processed to selectively remove components from the generatedreplacement fluid. The processed blood can be combined with thereplacement fluid and returned to the patient.

In another embodiment, dialysate can be recycled in a two-stage blooddialysis system. Typically, dialysate is disposed of after a single runthrough a dialysis device, such as filtration device 110, once it hasbeen contaminated by waste products. As a result, prior art dialysisdevices suffer from many of the same inefficiencies discussed above withrespect to filtration devices; large volumes of replacement dialysateare necessary, and large volumes of waste are generated. Instead,according to one embodiment of the present invention, the dialysatecontaining the intermediate weight waste products can be sent through asecond filtration device, such as one of filtration devices 10 or 110,in order to separate the waste products from the dialysate. The recycleddialysate emerging as filtrate from this second filtration device canthen be used in further dialysis procedures.

FIG. 8 is a schematic illustration of such a two-stage blood dialysissystem, wherein clean, recycled dialysate is generated from wastedialysate, reducing the need for large volumes of replacement dialysisfluid. As above, the directions of the flows of various fluids flowingthrough the system are illustrated by arrows.

A patient is represented by the box 300 farthest to the left. In atypical implementation, the patient 300 has characteristics similar tothose discussed above with respect to patient 200. Alternatively, thetwo-stage system may be used in an industrial setting, in which thefiltered fluid is some heterogeneous mixture from which intermediatesized molecules must be extracted.

The device comprising the first stage of this two-stage blood dialysissystem is hemodialysis device 310. As is well-known to those of skill inthe art, the filtration membrane used in the device 310 can have a widevariety of characteristics and can be chosen to filter any of a numberof differently sized particles. In one embodiment, the hemodialysisdevice 310 is configured to allow only those molecules having a weightof 10,000 Daltons or less to diffuse across the membrane.

In general, a hemodialysis device, as discussed above, has two liquidsrunning therethrough, one on either side of a filtration membrane. Sinceaqueous solutions are present on both sides of the membrane, the volumesof the liquids stay roughly the same, but the molecules therein tend toequilibrate across the membrane, as long as they can diffuse through.Thus, dialysate, having a relatively high concentration of electrolytes,salts, and other small desirable molecules, may be sent along one sideof the filtration membrane, and the patient's blood, having a highconcentration of waste by-products, may be sent along the other side ofthe filtration membrane. The two solutions will move towards equilibriumwith respect to the molecules that can diffuse across the membrane, andthe result will typically be a solution of dialysate and waste products,and processed blood with additional small desirable molecules.

The device used for the second stage of this two-stage blood dialysissystem may be described as an ultrafiltration device 320, so calledbecause it is permeable to smaller molecules. In a preferred embodiment,the purpose of the ultrafiltration device 320 is to filter out theintermediate weight, toxic molecules from a heterogeneous solution,leaving only the dialysate and other small desirable molecules. In thepreferred embodiment, the filtration membrane used in theultrafiltration device 320 is chosen to allow molecules having a weightless than approximately 300 Daltons to pass, thereby separating thepotentially toxic molecules from the rest of the solution. In otherembodiments, the filtration membrane may only allow molecules having aweight less than approximately 200 Daltons to pass, preventing other,possibly toxic molecules from emerging as filtrate.

The same or different types of filtration devices may be used for thehemodialysis device 310 and ultrafiltration device 320. As is well-knownto those of skill in the art, a number of possible hemodialysis devicesand filtration devices may be used. In a preferred embodiment, thehemodialysis device 310 is a Taylor vortex-enhanced filtration devicethat functions similarly to the filtration device 110 described abovewith reference to FIGS. 5 and 6. The ultrafiltration device 320 ispreferably a Taylor vortex-enhanced filtration device similar to thefiltration device 10 described above. As described above, thesefiltration devices may have any combination of a variety of sizes,shapes and speeds for their respective rotors and housings, in order toaccommodate the different viscosities and flow rates of the processedfluids.

A waste bag 330 is used to collect the undesirable waste productsproduced by this two-stage blood dialysis system. In one embodiment,this waste bag 330 should collect many of the same waste products thatwould normally be collected by a healthy kidney. Of course, the wastebag 330 may represent any of a number of means for collecting and/ordisposing of waste and need not be a physical receptacle of anyparticular shape or size. Often, the waste bags 330 must be collected ashazardous waste for careful disposal according to applicable laws andregulations. Due to the unique features of the present invention, thevolume of the waste products generated by the two-stage blood dialysissystem may be far less than that generated by a typical single-stagehemodialysis procedure.

Dialysate source 350 is shown with dialysate flow 355 entering thehemodialysis device 310. In one embodiment, the dialysate flow 355entering the hemodialysis device 310 is roughly equivalent to the bloodflow 365 from the patient. Thus, the processed blood flow 375 back tothe patient 300 is not substantially reduced in comparison to the flowfrom the patient. As discussed above, the dialysate flowing through thedevice 310 will travel along the other side of a filtration membranefrom the blood flowing through the device 310. In order to encourage thediffusion of waste products and prevent blood contamination, thedialysate should be sterile, pyrogen-free and generally at bodytemperature.

In a preferred embodiment, the dialysate is supplemented with a varietyof additives. Typical additives include biologically desirablecomponents, such as chloride, sodium, calcium, magnesium, potassium,phosphate, dextrose, and glucose, or any other molecule required by theparticular patient. These smaller molecules can diffuse across thefiltration membrane into the processed blood returning to the patient.

Using the two-stage blood dialysis system illustrated in FIG. 8, amethod of performing blood dialysis according to the present inventionmay now be discussed in further detail. The first step in the procedureis drawing blood from the patient, illustrated by the arrow 365extending from the patient 300 to the hemodialysis device 310.Conventionally, blood is drawn from the patient 300 via an IV tubeconnected to a patient's artery in the patient's arm. Of course, othermeans of drawing blood from a patient are well-known to those of skillin the art. As discussed above, a typical rate of blood flow from thepatient is 300-450 mL/min. In order to keep the patient's blood volumerelatively constant, therefore, the fluid returning to the patient,arrow 375, should flow at a similar rate. Conventionally, the fluidreturning to the patient 300 is returned through an IV tube connected tothe patient's vein.

The blood that is flowing from the patient 300 is then passed throughthe hemodialysis device 310. The hemodialysis device 310 may dialyze theblood in a number of ways well known to those of skill in the art. In apreferred embodiment, the hemodialysis device 310 works similarly to thedevice 110 described in detail above. In this implementation, the bloodflows into the first gap 116 through the inlet port 122. Dialysate flowsinto the second gap 146 through the inlet port 126.

The filtration membrane 118, separating the second gap 146 from thefirst gap 116, is designed to allow molecules with a molecular weightless than approximately 10,000 Daltons to pass in either direction. Theblood flowing from the patient 300 has a number of constituents,including: water, electrolytes, small nutrient molecules, wasteproducts, high molecular weight molecules (e.g. proteins, etc.) andblood cells and other cells of various types. The dialysis fluid flowingfrom the dialysate source 350 includes water and other small desirablemolecules that might supplement the patient's processed blood. Thus, asthe dialysate and blood flow in opposite directions through thehemodialysis device 310, the blood accumulates the small desirablemolecules diffusing from the dialysate, and the dialysate accumulatesthe waste products diffusing from the blood.

Meanwhile, the rotors 144, 114 spin rapidly in order to create Taylorvortices in both the blood flowing through the first gap 116, and in thedialysate flowing through the second gap 146. These Taylor vortices mixthe fluids in both gaps and thereby alleviate the problems ofconcentration polarization on the outside and inside of the filtrationmembrane 118.

The filtration device 310 has two outlet ports, 124 and 128. The firstoutlet port 124 communicates with the first gap 116. Because very littlewater diffuses across the filtration membrane 118 (since the dialysateand blood have relatively equivalent flows), in a typicalimplementation, the flow rate from this outlet port 124 is roughly equalto the flow rate into the inlet port 122. If there are smalldiscrepancies, they can be rectified using supplemental replacementfluid or by removing a small quantity of the processed blood beforereturn to the patient.

The second outlet port 128, which is in communication with the secondgap 146, conducts the flow of waste dialysate 385. This waste dialysate385 enters the ultrafiltration device 320.

As described above, the ultrafiltration device 320 may functionsimilarly to the filtration device 10. The filtration membrane 18 of theultrafiltration device 320 is configured such that the dialysatesubstrate and small desirable molecules enter the rotor interior 20 ofthe ultrafiltration device 320. The intermediate weight waste productsare filtered out and pass from the ultrafiltration device 320 to thewaste bags 330. The filtrate, meanwhile, now comprises a clean, warm,bio-compatible dialysate that can be used once again to diffuse wasteproducts from the patient's blood.

Since the concentration of small desirable molecules in the dialysatehas been depleted by diffusion into the patient's processed blood, thesemolecules may be supplemented from a small desirable molecule source390. In a preferred embodiment, the system may detect the flow ofdialysate and add appropriate amounts of concentrated liquid to therecycled dialysate through a T-junction.

In the embodiment shown in FIG. 8, the recycled dialysate 395 isintroduced at the beginning of the two-stage filtration system, where aT-junction combines the recycled dialysate 395 and the new dialysateflow 355. Ideally, very little unused dialysate will be needed once thesystem has gone through a complete cycle.

In variations of the embodiments illustrated in FIGS. 1-8, thisinvention can be applied to a vast number of other applications. In ageneral sense, embodiments of this invention can be useful in anyapplication where filters lose performance due to clogging orconcentration polarization, and where replacement fluid is desirable.These applications include: removal of salt from water, processing seawater for human consumption, processing sea water for agricultural uses,reprocessing waste water for agricultural uses, reprocessing waste waterfor human consumption, concentrating sugar or other desired componentsfrom sap from plants, such as sugar cane sap or maple sap, concentratinglatex from the sap of rubber plants, removing impurities from water forindustrial applications, such as needed in the pharmaceutical orelectronic industries, recycling cooking oil, recycling motor oil orlubricating oils, and producing sterile water for intravenous injection.

Further, where molecular exclusion or sieving membranes are employed,the device can be used for large scale cell and biotechnology separationapplications, such as purifying cell supernatants and/or lysates fromcellular material in a bioprocessor or fermentor.

The various materials, methods and techniques described above provide anumber of ways to carry out the invention. Of course, it is to beunderstood that not necessarily all objectives or advantages describedmay be achieved in accordance with any particular embodiment describedherein. Thus, for example, those skilled in the art will recognize thatthe components of the system may be made and the methods may beperformed in a manner that achieves or optimizes one advantage or groupof advantages as taught herein without necessarily achieving otherobjectives or advantages as may be taught or suggested herein.

Although the present invention has been described in terms of certainpreferred embodiments, other embodiments of the invention includingvariations in dimensions, configuration and materials will be apparentto those of skill in the art in view of the disclosure herein. Inaddition, all features discussed in connection with any one embodimentherein can be readily adapted for use in other embodiments herein. Theuse of different terms or reference numerals for similar features indifferent embodiments does not imply differences other than those whichmay be expressly set forth. Accordingly, the present invention isintended to be described solely by reference to the appended claims, andnot limited to the preferred embodiments disclosed herein.

1. A method of performing hemofiltration on a patient, comprising:providing a first filtration device, configured with a filtered bloodoutlet port connected to a filtered blood flow conduit; providing asecond filtration device configured to create Taylor vorticity,configured with a waste product outlet port; introducing blood from thepatient into the first filtration device via a blood inlet portconnected to a blood supply conduit; introducing a first filtrate via ablood waste outlet port connected to a blood waste flow conduit from thefirst filtration device into the second filtration device via a bloodwaste inlet port connected to the blood waste flow conduit; andobtaining a replacement fluid from the second filtration device via areplacement fluid outlet port connected to a replacement fluid flowconduit.
 2. The method of claim 1, further comprising the step of:connecting the replacement fluid flow conduit to the filtered blood flowconduit.
 3. The method of claim 1, further comprising the step of:connecting the replacement fluid flow conduit to the blood supplyconduit.